Injection molding of ceramics has been described by several authors in the open literature (e.g. T. J. Whalen et al., Ceramics for High Performance Application-II, Ed. J. J. Burke, E. N. Lenoe, and R. N. Katz, Brook Hill Publishing Co. 1978, pp. 179-189, J. A. Mangels, Ceramics for High Performance Application-II, pp. 113-129, G. D. Schnittgrund, SAMPE Quarterly, p. 8-12, July 1981, etc.) and in patent literature (e.g. M. A. Strivens, U.S. Pat. No. 2,939,199, 1960, I. A. Crossley et al., U.S. Pat. No. 3,882,210, 1975, R. W. Ohnsorg, U.S. Pat. No. 4,144,207, 1979, etc.). Several papers have also been published by GTE authors (e.g. C. L. Quackenbush et al., Contractors Coordination Meeting Proceedings, 1981, G. Bandyopadhyay et al., Contractors Coordination Meeting Proceedings, 1983). The general process routing for injection molding is well known. It includes (a) compounding which involves mixing the high surface area ceramic with molten organic binder, (b) injection molding by which the powder/binder mix is formed into a given shape in a metallic mold, (c) binder removal which must be accomplished without disrupting the ceramic structure, and (d) consolidation of the part by sintering and/or by hot isostatic pressing. Significant effort has been made by various researchers to determine the effects of starting powder particle size and size distribution on moldability of powder, and to identify binder systems that allow easy compounding, molding and binder burnout (without disruption) from the part. Although volumes of patent literature now exist on powder requirements, different binder concepts and binder removal processes, it is generally recognized that injection molding and binder removal from a large, complex cross section part (e.g. rotors for turbine engines) poses a very difficult task because of internal and external cracking during burnout. An extensive evaluation of the patent literature reveals that in most cases only small cross section (less than one centimeter) parts were considered as examples, or that the cross sections and complexities were not revealed. None of these references described fabrication of large, complex cross section silicon nitride parts, specifically fabricated by injection molding and sintering. GTE Laboratories has developed a process routing which is highly successful for fabrication of good quality small cross section injection molded and sintered parts, such as turbine blades and vanes, in large quantities. Since this development, improvements in binder composition (K. French et al., U.S. Pat. No. 4,456,713) allowed further simplification of molding and binder removal procedures. This process routing however, failed to produce an externally crack-free injection molded ceramic article having a large cross section one centimeter or greater (e.g. turbine rotor and turbocharger sized test parts). It has been established that the use of a submicron starting powder, such as silicon nitride containing Y.sub.2 O.sub.3 and Al.sub.2 O.sub.3, and a binder results in certain fundamental difficulties which causes external and internal cracking in large cross section parts.